Blightbelly Rat is a common Creature — Phyrexian Rat card from Phyrexia: All Will Be One (ONE), collector number 289. Current market price: $0.27 (foil $0.26), TCGplayer market prices via Scryfall.
Toxic 1 (Players dealt combat damage by this creature also get a poison counter.) When this creature dies, proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)